How Gluten Sensitivity Is Diagnosed

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Getting a gluten sensitivity diagnosis isn't a straightforward process. Medical research lends support to the idea that non-celiac gluten sensitivity is a real condition, but there are physicians who do not believe in its existence. Furthermore, there is no consensus on how to test for gluten sensitivity or what results of tests used by some when working toward a diagnosis actually mean.

Keep in mind that most physicians recommend you undergo celiac disease testing first if you suspect you are reacting to gluten. However, if your celiac disease test results are negative, gluten sensitivity tests may provide you with evidence that your body is mounting a response to gluten.

At-Home Testing

Direct-to-consumer test kits are available that test stool or a finger-prick blood sample for various food sensitivities, including gluten. However, the testing methods used have not been proven to reliably identify food allergies, food intolerances, or gluten sensitivity.

Test kits such as Everlywell (pitched on the TV series "Shark Tank") test for IgG antibodies, which are a poor indicator of food intolerance. Allergy professional organizations in Europe, Canada, and the United States warn that many people without food allergies or intolerances will test positive with these kits, which could lead to unnecessarily restricting healthy foods and won't help diagnose a food intolerance.

EnteroLab gluten sensitivity testing is marketed directly to consumers, using a stool sample. Enterolab's stool testing looks for antibodies to gluten directly in your intestinal tract. However, its testing protocol, developed by gastroenterologist Kenneth Fine, MD, has yet to undergo outside scrutiny and verification.

What's more, Dr. Fine has come under considerable criticism from other physicians and from people in the celiac/gluten-sensitive community for failing to publish his research and results. As a result, few physicians will accept EnteroLab testing as proof of gluten sensitivity.

Consumers should be wary of home testing kits for gluten sensitivity as they often give false-positive results and do not use testing methods approved by clinical authorities.

Labs and Tests

Before gluten sensitivity can be diagnosed, celiac disease must be ruled out. Physicians generally being this process by using a panel of celiac blood tests to look for the antibodies that indicate the condition. There is some evidence that two of those tests—the AGA-IgA and the AGG-IgG—could indicate non-celiac gluten sensitivity as well. However, there is currently no blood test that is specific for gluten sensitivity.

Alessio Fasano, MD, head of the University of Maryland Center for Celiac Research, says that the AGA-IgA and AGA-IgG blood tests only serve as surrogates and that there is no specificity there. The fact that about half of gluten sensitivity patients tested negative for these antibodies makes those two tests much less useful as tests for gluten sensitivity, notes Dr. Fasano.

Gluten-Free Diet and Gluten Challenge

Because there is no blood test or other biomarker tests that can diagnose gluten sensitivity, the best method is using a symptom questionnaire and a gluten challenge. The criteria developed by the Salerno Experts' Panel is primarily used for research, but it can be used in a clinical setting:

  1. Eat a normal gluten-containing diet for at least six weeks and rate your symptoms on a numerical rating scale.
  2. Go on a strict gluten-free diet for at least the next six weeks (preferably with consultation of a dietitian). You rate your symptoms weekly. Response to the gluten-free diet is defined as a greater than a 30% reduction in one to three of your main symptoms in at least three of the six weekly evaluations.
  3. See your doctor for a gluten challenge: In a research setting, this is done with a double-blind, placebo-controlled crossover challenge. For a clinical setting, it could be single-blinded and you wouldn't know whether you've been given gluten, but the doctor would.

For a gluten challenge, you take a dose of 8 grams of gluten (or placebo) daily for one week while otherwise maintaining your gluten-free diet. The gluten (or placebo) is provided in an edible such as a muffin, bar, or bread. You report on your symptoms with the questionnaire.

There is a one-week washout period, followed by a challenge again, this time with the opposite dose (placebo or gluten) and reporting of symptoms. Likewise here, if there is a variation of 30% between the gluten and placebo, it can indicate gluten sensitivity. If not, other causes of the symptoms should be explored.

Differential Diagnoses

Gluten sensitivity can only be diagnosed after ruling out celiac disease and food allergies, especially wheat allergy. While these three conditions are all treated with a gluten-free or wheat-free diet, they have some important differences.

Celiac disease is a genetic, autoimmune disease that damages the lining of the small intestine and can lead to malabsorption of nutrients. It has a large number of symptoms and can be diagnosed with blood tests and endoscopy/biopsy of the small intestine. Endoscopy/biopsy might be done if celiac disease is suspected, but will not show any irregularities in gluten sensitivity.

Wheat allergy is an immune system response to the proteins in wheat. When a person has a food allergy to wheat, their body's immune system sees the proteins in wheat as invaders and initiates an allergic response, which can result in hives, swelling of the lips and throat, and, in extreme cases, anaphylaxis. The reaction to wheat happens very fast in wheat allergy, with symptoms in minutes to a few hours.

A person with wheat allergy may be able to have gluten from non-wheat sources, unless they also have celiac disease or non-celiac gluten sensitivity. Children may outgrow a wheat allergy, but in adults it usually persists for life.

Non-celiac gluten sensitivity doesn't have the autoimmune markers or allergy markers seen in celiac disease and wheat allergy, and doesn't show the typical damage to the small intestine seen in celiac disease. The symptoms develop slowly (in two or more days) after exposure to gluten, rather than rapidly, as seen with wheat allergy.

Finally, there are some connections between gluten sensitivity and irritable bowel syndrome that will need to be explored by your doctor as well. For this reason, it is extremely important that you talk to your doctor about your symptoms if you feel you are reacting to gluten.

A Word From Verywell

Testing for gluten sensitivity is still in its infancy. The diagnosis is based on excluding other conditions and assessing the reaction to a gluten-free diet and gluten challenge. There is no reliable at-home test and blood tests are primarily done to rule out celiac disease and other conditions. If medical researchers can agree on criteria for the condition, it is likely that better, more accurate options will be developed in the future.

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  3. Catassi C, Elli L, Bonaz B, et al. Diagnosis of Non-Celiac Gluten Sensitivity (NCGS): The Salerno Experts' Criteria. Nutrients. 2015;7(6):4966–4977. Published 2015 Jun 18. doi:10.3390/nu7064966

  4. Sapone A, Bai JC, Ciacci C, et al. Spectrum of gluten-related disorders: consensus on new nomenclature and classification. BMC Med. 2012;10:13. doi:10.1186/1741-7015-10-13

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